1. Field of the Invention
This invention relates generally to breathing apparatus for clean room environments, and relates more particularly to an in-line silencer for use with such breathing apparatus.
2. Description of the Relevant Art
Workers in clean rooms, surgical operating rooms, or other controlled environments are a source of contamination. A living, breathing person exhales hundreds of microscopic particles per minute. A smoker can exhale large quantities of particles for quite some time after smoking. Facial skin, cosmetics, and eye emissions are also sources of contaminating particles.
Masks made of fabric or foam are not very effective in containing such particulates. Consequently, clean room breathing apparatus have been developed which contain particles generated by the workers and prevent the particles from entering and thus contaminating the clean room environment.
A typical clean room breathing apparatus includes a headgear assembly with a hood or other accessories, generally having a clear face shield for viewing, and an air blower coupled to the headgear assembly through a connecting hose or duct. The air blower exhausts air contaminated with particles from the headgear assembly. The air blower in effect causes a slight vacuum within the headgear assembly so that particles generated by the worker are carried away by the air exhaust and do not enter the clean room. Replacement air enters the headgear assembly from the clean room. Located on the exhaust side of the air blower, a HEPA (High Efficiency Particulate Air) filter traps particles exhausted by the air blower so that they do not enter the clean room environment.
A variation of the above-described breathing apparatus has a second air blower that supplies air to the headgear assembly. The supply blower is similar to the exhaust blower, and has a separate hose or duct that carries air to the headgear assembly. Exhaust air, contaminated with particles generated by the user, is exhausted by the exhaust blower.
One problem that has developed with prior clean room breathing apparatus is that the noise generated by the air blower or blowers can impede communications among workers. To overcome this communication problem, some have gone to great expense to install electronic communication devices such as voice amplifiers. Another factor is that, since clean rooms have become quieter, the noise generated by the breathing apparatus has become more noticeable in comparison.